Ceiling system

ABSTRACT

In order to prevent buckling or excessive displacement or deflection of ceiling support members in a fire, a gap is left between ceiling support members but the ceiling support members are secured together and positively spaced apart by a spacing and supporting arrangement which includes fusible material so that in a fire, the fusible material will melt and allow the width of the gap to alter while at least one of the support members remains supported on the other. This prevents collapse of the ceiling and improves the fire resistance of the building.

United States Patent- 1191 3/1967 Van Der Sluys et al ..52/665 Bailey et al. 1451' Jan. 9, 1973 541 CEILING SYSTEM v 3,321,879 7 5/ 967 [75] Inventors: Malcolm Bailey, Alresford; John 1 Colin Downer, Chandlers Ford, 'fog jggo 41/1962 both of England 3 243 339 5/195 [7 3] Assignee: Conder International Limited, g'ggiggg- 3x322 Lickliter 52mm 5 Winchester Hampshire England I [2'2] Filed: June 3, 1970 FOREIGN PATENTS OR APPLICATIONS 1,021,555 12/1957 Germany ..,.287/189.36,A [21] Appl. No.. 43,130 1,005,866 9/1965 Great Britain... ..'..52/665.

7 109,227 7/1964 Netherlands ..52/665 [30] Foreign Application Priority Data Przmary Examinerl-lenry C. Sutherland June 4, Great Attorney cfaig & Antonni 52' U.'s.C1.' ..52/232, 52/484, 52/489, 57 B TRA T p 1 52/495, 287/189.36 A 1 In order to prevent bucklmg or excesslve d1splacement 51 111801.... ..E04.2/00 or deflection of Gem Su on members in a fire a [58] Field of Search ..52/484, 488, 489, 495, 665, a is left between cflin on members but-{he 52/669, DIG. 5, 232; 287/l89.36 A; 85/5; 3 I}. t b g PP d t th d 24/73 P ce11ng suppor mem ers are secure oge er an I posmvely spaced apart by a spacmg and supportmg ar- 56 1 d rangement which includes fusible material so that in a l 1 Fm- C"? H fire, the 81511518 material will melt and allow the width UNITED STATES PATENTS of the ap to alterwhile at least one of the support I V members remains supported on the other. Th1s 2,718,290 9/1955 Segil ..52/232 prevents collapse of the ceilingand improves the fire 3,089,570 5/1963 ONeil ..287/189.36 A resistance f the building 8 I 3,232,021 2/1966 Wiison...'. ..287/l89.36A 5 I 3,309,122 17 Claims, 11 Drawing Figures PATENTEDJAH 9197s SHEET 1 [IF 5 INVENTORS MALcmM emu-1v mo mu couN new!!! 9 w GE ATTORNEYS 'PATE NIEDJM 9 ms SHEET 2 BF 5 FIGS INVENTORS MALCOLM BAILEY AND J'OHN couu nob MGR ATTORNEYS P-ATENTEDJAN 9 1975 SHEET 3 BF 5 INVENTORS MMcoLM BAILEY AND JOHN col-m Dov/MGR C-vnij, qnrinelli, Sham-f1 Hm ATTORNEYS PATENTEDJAH 9 191a SHEU t 0F 5 INVENTORS MALcoLM amusi mo Tom couN oownea Cw RnBnQlH, summit H-ll AT TO RNEYS PATENTEIJJAN 9 I975 3,708,932

SHEET 5 BF 5 0 .mm FIG. 8 5

IGII

W58 7 F v 5 INVENTORS MALCOLM BAILGY MD T NN U UN nouluER cvm wfinlonelli, smwt mll ATTORNEYS 1 CEILING SYSTEM This invention relates to a ceiling system for a building and particularly, but not exclusively, to a suspended ceiling system, and can be applied to the system described'in British Patent Specification No. 1,154,081 the description of which is incorporated herein by reference. Normally, ceiling systems, and suspended ceiling systems in particular, provide a ceiling which has either insulation qu'alities, decorative qualities, sound absorption qualities, fire protective qualities, or

a combination of these properties, and is suspended from the floor above, or roof, using straps or hangers. The ceiling is usually supported on either T-section, bulb T-section, or I-section bearers, and uses either an exposed or secret method of fixing. The ceiling can be supported at a large number of points, and it is an object of the. invention to arrange the ceiling so that both I under normal conditions and in a fire, displacement or deflection of the ceiling supportmembers can be within acceptable limits. In a fire, the ceiling should remain as flat and as dimensionally stable as possible in order that gaps should not occur, nor ceiling panels fall out.

According to the invention, a gap is left between the end of oneceiling support member and the adjacent part of another ceiling support'member, the ceiling support members being secured together and positively spaced apart by a spacing and supporting arrangement which includesfusible material so that in a fire, the fusible material will melt and allow the width of said gap to I alter whilst at least the first-mentioned ceiling support member remains supported on the other ceiling support member; the ceiling support members may remain mutually supported on each other.

According to the invention, a gap may be left between the adjacent ends of adjacent, aligned ceiling support members with the ceiling support members secured together and positively spaced apart by a spacing arrangement which includes fusible material so' that in a fire, the fusible material will melt and allow the sec- ;tions to move axially with respect to each other whilst remaining secured together as regards substantial relative movement in other directions. The spacing arrangement may include a longitudinal spacing member .which' spans said gap, the spacing member being secured to each ceiling support member as regards longitudinal movement, a fusible securing member (e.g. a peg-like member inserted through'registering apertures in the spacing member and in-the'ceiling support member) being used to secure the spacing'member to at least one of the channel sections. The spacing member can lie along the top of the ceiling support dency of the channel sections to buckle is' reduced or prevented.

According to this invention, a'ceiling system may have two parallel sets of members, a first set of which:

generally parallel main members and a second set of subsidiary, members interconnecting (and preferably generally at right angles to) the first set of members, the sets of members being secured together by securing devices formed of or including fusible material so that in a fire, the fusible material will melt and allow the sets of members to move with respect to each other, the sets of members and securing devices being arranged such that the subsidiary members are slidably supported by the main members when the fusible material melts. One simple way of achieving this is to have the end portions of the subsidiary members resting on external support surfaces provided by projections on the main members. If the members are channel sections, they may have sidewalls having their lower portions curved inwards through approximately 90 and then downwards and outwards through approximately 180 to continue as outwardly-projecting lips. I

The securing device maybe just a clamp for clamping the relevant members together. One useful clamptype securing device is a bridge shaped (i.e. generally inverted U-shaped) member whichspans the main member and holds the subsidiary member down. The

bridge-shaped securingdevice may have a part for engaging in adetent on the end portion of the subsidiary member, conveniently, on the top of thesubsidiary member. The detent may be a transverse slot in the subsidiary member, for instance cut with a saw. The upright of the bridge maybe ofhollow section and open at the bottom-so that the outer-wall (the wall remote from the main member) can act as said part and enter the detent. The securing device is preferably snap-fitted into position. One possible snap-fitting is to have at least one resilient, ratchet-type projection on the securing device which engages in an aperture in the main member. If the main member is an inverted channel section and the securing device is bridge-shaped, the projection(s) may engage in an aperture in the top of the section. I

The fusible material may be plastic, and in general, the fusible material preferably melts below 200 C. I I

The invention will be further described, by way of example, with reference to the accompanying drawing, of

FIG. 1 is a perspective view, partly in section and partly broken away, of a ceiling system in accordance with the invention; I l I I I FIGIZ is a cross-section through a channel section in accordance with the invention, showing a closure panel, a bridge member and a pipe conduit;

FIG. 3- is a cross-section through a connection between two aligned channel sections;

FIG. .4is a side view of two channel sections connected together; I

FIG. 5 is a cross-section through a channel section showing how the interconnecting members are secured;

FIG. 6 is a similar cross-section to FIG. 5, showing a slightly different arrangement;

FIG. 7 is a top view ofa spacing bar shown in FIGS. 3 to 6; and

FIGS. 8 toll illustrate four different ways of fixing theceiling panels inposition, each Figure showing two partial sections along two 'verticalplanes at right angles to each other, one partial section being taken through 3 thechannel'section and the other partial section'bein'g taken through a Tvbar.

The suspended ceiling system ,of FIG.- 1 has metal, cold-rolled channel sections 1, which forma grid'with subsidiary T-bars 2, extending at right angles to the sections '1. The ends of the T-bars 2 are notched or rebated I at 3 (see FIGS. 6) and have cut-outs 4 (FIG. 5) so that the ends, of the T-bars can either rest on lips 5 of the of the T-bars 2.

The building has a main beam 25 which supports a concrete floor unit26. Either (a) chevron-slotted angle strips 27. are attached to the floor units 26 by means of hook. bolts 28 and the channel sections 1 are suspended from the angle strips 27 by means of suspen I sion rods. 29 (as shown) or (b) the channel sections 1 are suspended direct from .the floor units, 26 (not shown). Apertures or deliniated apertures (scored or pressed rings in the surface of the metal which can easily be knocked out) are provided in the top of the-chan-'.

nel' sections 1 and are used toattach the suspension rods 29 direct to thechannel sections 1 I As can be seen inoreclearly in FIGS 4-6, the T-bars 2 are secured in position by bridge shaped-T bar connectors6'which areformed of a fusible material such as self-extinguishing nylon (nylon including a flame-retardant): The connector6 spans the channel section 1 and two ratchet-type projections 1 7 (forming 'a peg-like member) have been inserted through a circular hole; in the'top of the channel section I and hold the connector 6 securely in position. As can be seen in FIGS. Sand 6, the'upright 8 of the connector 6 is of hollow section and its outer-wall 9 engages in a cut-out It) in-thetop of the endportion of the T-bar 2, securingthe T-bar 2 against movement away from the channel section 1.

The cross-section ofthe channel section I can be 'seen'in FIG. 2. The top has each edge portion curving downwardsthrou gh approximately 90, to continue as a respective sidewall. The lower portion'of the sidewall curves inwards through approximately 90 and then downwards and outwards through approximately l80 to continueflas the o'u twardlyprojecting lips. The inwardly-directed portions of the sidewalls provide internalsupportsurfacesl2. As shown in FIG. 2, the internal support surfaces 12 may be used to support closure panel in theform of a snap-fitted plastic strip 13 (e.g.

formed of stiff, polyvinyl chloride) for closing the chan-' nel section "1. Bridge members l4' may'be provided at intervals along the channel section I forsup porting services such as electrical wiring. V

The section 1 shown in FIG. 2 is cold-rolled from a 200 mm wide steel strip. Y I

The lengths of channel section I are joined together by sleeves 15 whose lower lips engage under the support surfaces 12L The sleeve 'isclamped by a bolt 16 running across in agap betweenthe ends of the channel sections 1, theiclarnpbeing not-sotight as to prevent longitudinal sliding movementofthe channel sections 1 if a tire occurs. A spacing member in the form of a spacer bar 17 (see. FIG. 7) lies along the top ofthe channel. section 1;. The spacer bar 17'locates the channel: sections longitudinally; the projections 7 on the connectors 6 on either side of the connection pass down through respective registering holes'in the end portions of the spacer bar and in the tops of the channel sections 1. Earth continuity is provided by spacer ha and by the sides and bottom lips of the sleeve 15. Y

Ceiling panels 18 are supported by the lips 5 of the. channel sections 1 and by the bottom flanges of the T- bars 2. A choice of five different arrangements for the ceiling panel is provided, asfollows:

i. The channel section lips 5 and the T-bar'flanges are exposed (see FIG. 8 I I ii. A full secret fix is provided, the panels 18 passing under the channel sections 1 but the flanges of the T- bars 2 engaging .in side grooves in the ceiling panels 18, the T-bars 2 being lower than the channel sections asin FIG. 6 (see FIG. 9).

iii. A semi-secret fix is provided, the channel section v lips5 being exposed but the flanges of the T-bars 2 en- I .gagingin side grooves in the ceiling panels 18, the T;

' bars2 being higher in relation to the channel section I edges of the ceilihg'panels being rebated where they rest on the channel section lips 5 (see FIG. ll and FIG. 2).

v. The ceiling pan'els 18 are not rebated but have sliding bolt-like catches on their upper surfaces for book ing over the channelsec tion lips 5 and the. flanges on the T-bars2 the ceiling panels l8 providing a continu-v ous ceiling beneaththe channel sections 1 and the bars 2 (see-FlG..3,).

lnany of these arrangements, abutting edges of ceilingpanelscan be grooved and metal strips in the form of splines or even small T-bars canbe inserted in the groovesto align the ceiling panels properly; if small T.

bars are used, their endportions can be slightly joggled (displaced upwards) and rest on the flanges of the T- bars 2. The ceiling panelscan .be tiles of any suitable type, for instance mineral fiber board or asbestos board. I I H light tittingclip 2 0 is shown in FIG. 1, clipped to the lips 5 ofthe channel section 1'. I j I Pipe conduits 22 (seeFlG. 2) extend between adjacent channel sections, 1 and provide earth continuity and a conduit for services.'An inspection Tee 23 is used for connection and a'male bush 24 is screwed up through an aperture in the top of the channel section 1 so I and into the Tee. I

FIG. 1 shows a partition 30,- and FIG. 5 shows the mounting in more detailJA retaining bar 31 rests onthe 1'. A ceiling support system-comprising: a set of substantially parallel main ceiling support members of inverted channel section configuration, a set of subsidiary ceiling support members interconnecting said main members, primary ceiling-support means for holding said main and subsidiary members in a horizontal "6'. A system according plane, supporting guide means for guiding relative movement between the respective main and subsidiary members in said horizontal plane, said supporting guide means including means for slidabliy supporting the Subpredetermined distance from one another to form a gap between the end of the subsidiary member and the side of the main member, said spacing means being located in position on the main member by way of aperture 7 means in the upwardly facing side of the main member and being interconnected with said subsidiary member by interengagement with top portions of said subsidiary member such that said spacing means can be attached from thetop-to respective subsidiary and main meme 6 least two adjacent support members for spacing said at leasttwo adjacent support members a predetermined distance from one another to form a gap therebetween, and supporting guide means for guiding relative movel'l'lefli between the at least two adjacent support membe'rs in a horizontal plane, said spacingmeans including structure constructed of a relatively more fusible material than said support members and said supportb'ers after they are held in place in their final assembled I positions by the primary ceiling support members, said spacing means being constructed of a relatively more fusiblematerial than said support members and said supporting guide means such that melting of the fusible structure of the spacing means inthe event otla fire will permit the ends of subsidiary members to, move in a horizontal plane in the direction of the main'mernbers to thereby reduce the risks of buckling and collapse of ing guide means, whereby the fusible structure oi the spacing means will melt in the event of a tire permitting the adjacent support members to move in a horizontal plane relatively to one another thereby reducing the risks of buckling and collapse of the ceiling system,

wherein at least one of said gaps is located between adjacent ends of adjacent aligned ceiling support members, wherein said spacing means-and said supporting. guide means include means 'for permitting relative movement of the aligned ceiling support members in a single axial direction while preventing substantial relative movement in directions other than said axial direction, and wherein said spacing means includes a longitudinalspacingmembers spanning said gap and a fusible. securing member for securing the spacing member to at least one of said ceiling support mem bets, said spacing member operative ly engaging both of said adjacent ceiling support members to normally hold said ceiling support members in a fixed position with respect to one another. Q 3 n 1 i 8. A system according to claim 7, characterized. in

' that said spacing member and oneof said'ceiling sup spanning a "respective main member'and holding at least'one subsidiary member in position with respect to said main member. g Y

v3. A system according to claim 2, characterized in thatgaps are formed between ends of the subsidiary members and edges of said main members .at the respective junctions and between theends of respective aligned main members at positionsspaced from the respective junctions, saidspacing means andsaid supporting'means further-including means for permitting relative movement of the aligned main members in a single axial direction while preventingsubstantial relative movementof the main members in directions other than said axial direction. I i

4, A system according to claim 2, characterized'in that said bridge shaped member includes a part forengaging in a detentprovided on an end portion of saidat least one subsidiary member.

I 5'. A system according to claim 4,1 characterized that said bridge shaped member includes uprights of hollow sectionf which are open in *the, downward direction, the part for engaging the detentbeing af'wall I of said hollow section disposed away'from saidmain member. a a

to claim 1, characterized in that means are provided forsnap-fitting said spacing means into position onsaid ceiling supportmembers,

. and in that at least one resilient ratchet-type projection isprovided on said spacing means for engagement with the aperture means of said ,main ceiling .support member.

' 7..A ceiling;.support system comprising a plurality of ceiling support members arranged forsupporting coilport members'have registeringapertures', and in'that said fusible securing members includes a pe'g lilse member inserted through said registering apertures. 9. A system according to claim 7, characterized in that said spacingmernber andsaid ceiling support distance from one another to form a gap therebetween, and supporting guide means for guiding relative moveme n t between the atleast two adjacentsuppo rtrnem bers in.a horizontal plane, said spacing meansincluding structure constructed or" a relatively more fusible material than said support members and said support: ing guide means, whereby the fusible structure of the spacing means will melt in the event ofa tire permitting the adjacent support members to movein a horizontal plane relatively to one another thereby reducing the ing panels, spacing mean'soperatively connected tof at risks of buckling and collapse of the ceiling system, wherein at leastoneof said gaps is located between adjacent ends of adjacent'aligned ceiling support me'm .bers', wherein said spacing means and said supporting guide 1 means include means for permitting relative movementof'the aligned ceiling supportmembers'ina single axial direction whilepreve nting substantial relative m ovement in directions other than said axial direction, and .wherein said adjacentaligned ceiling support members are constructed as channel sections along a first axis, two subsidiary ceiling support members arranged atopposite sides of said main member and extending longitudinally along a second axis arranged at an angle with respect to the first axis, and a connecting means operatively connecting said main member toboth of said subsidiary members at a posh tion spaced from 'the ends of the 'main member, said connecting means including a-connecting member having a downwardly open U-shaped configuration straddling the main member such that a connecting leg is disposed on each of two opposite sides of said main member,-. that .:portion of the U-shaped connecting member between the'connecting legs being fastened to said main member by fastener ,means engaged in an i aperture on saidmain memben'each of said connecting legs being connected to attend of a respective subsidiary member by .wa of-detent means positionedon said subsidiary member and said connecting leg such that the respective ends of the subsidiary members are held in a predetermined distance from vertically extending outer surfaces onsaid main member; whereby the subsidiarymember can move alongthe second axis said predetermined distance .upon disengagement of the connecting means main members A 12.'A system according toclaim 11, characterized in that said main member is constructed as 'a three sided box-shaped channel member with the open side facing downwardly, said channel member includingoutwardly extending lip portions for 'slidably supporting bottom end'portions of said subsidiarymembersand in that prior to abuttingly engaging said said' firs't and second axes are substantially perpendicuQ lar to one another and are-"in a common horizontal plane.

1 -l3."A system according to claim 12; characterized-in thatsaid connecting member is constructed of: material that is more fusiblethanthe material of the ceiling support members. whereby during a tire the connecting member becomes inoperable and the subsidiary in'embersare permitted to slide freely on the lip portions in the directionof the vertically extending outer surfaces of the i'nain member.

14. A system according to claim 1 3, characterized in that said detent means include a cut-out recess portion n in the respective subsidiary members and an outer wall portion ofthe respective connector legs. 7

, 15. A system according to claim 14, characterized in I that said-fastener means includes a peg-like member having two resilient ratchet ty'p'e projections for engaging in an aperture at the top of the main member. i 16. A fusible securing device for securing a first ceiling support building member of a three sided rectangular box-shaped configurationwith the open side facing downwardly to two further ceiling support building members extending perpendicularly to and at opposite sides of said first member in 'such a manner as .to permit the "building members to move with respectjo one anotherupon melting of th'e f'ustble device in a fire; saidsecuring device being of a downwardly. open U-shaped configuration for straddling said first @member with securing legs of said device disposed at each of two opposite sidesof said firstmember, saiddevice-further including at least'one resilient ratchet-type projection extending downwardly from that portion of the device interconnectin g the securing .legsfor snap-fitting engaging in acorrespondingaperture at the top side of the first member, and each of said securing legs having detent parts for engaging with respective detents at the topiportions ofsaid further members for holding the distance upon further members a predetermined distance from vertically extending outer-surfaces at the sides of the first member; whereby said .device can be inserted from above onto said buildingmembers and whereby said further; members can move 7 saidv predetermined melting of said securing device prior to abutting engagement with'said first member.

17. A securing device'according to claim 16, wherein I saidvse'curing legseach includejuprights of hollow section and open at the bottom, and wherein said detent part is'anouter wall of said hollow section which is engageable in a detent on the end portion of the respec 

1. A ceiling support system comprising: a set of substantially parallel main ceiling support members of inverted channel section configuration, a set of subsidiary ceiling support members interconnecting said main members, primary ceiling support means for holding said main and subsidiary members in a horizontal plane, supporting guide means for guiding relative movement between the respective main and subsidiary members in said horizontal plane, said supporting guide means including means for slidably supporting the subsidiary members on the main members, and spacing means operatively connected to a respective main member and a respective subsidiary members for normally spacing said main and subsidiary members a predetermined distance from one another to form a gap between the end of the subsidiary member and the side of the main member, said spacing means being located in position on the main member by way of aperture means in the upwardly facing side of the main member and being interconnected with said subsidiary member by interengagement with top portions of said subsidiary member such that said spacing means can be attached from the top to respective subsidiary and main members after they are held in place in their final assembled positions by the primary ceiling support members, said spacing means being constructed of a relatively more fusible material than said support members And said supporting guide means such that melting of the fusible structure of the spacing means in the event of a fire will permit the ends of subsidiary members to move in a horizontal plane in the direction of the main members to thereby reduce the risks of buckling and collapse of the ceiling system.
 2. A system according to claim 1, characterized in that the spacing means includes a bridge shaped member for each respective junction of main and subsidiary members, each of said bridge shaped members spanning a respective main member and holding at least one subsidiary member in position with respect to said main member.
 3. A system according to claim 2, characterized in that gaps are formed between ends of the subsidiary members and edges of said main members at the respective junctions and between the ends of respective aligned main members at positions spaced from the respective junctions, said spacing means and said supporting means further including means for permitting relative movement of the aligned main members in a single axial direction while preventing substantial relative movement of the main members in directions other than said axial direction.
 4. A system according to claim 2, characterized in that said bridge shaped member includes a part for engaging in a detent provided on an end portion of said at least one subsidiary member.
 5. A system according to claim 4, characterized in that said bridge shaped member includes uprights of hollow section which are open in the downward direction, the part for engaging the detent being a wall of said hollow section disposed away from said main member.
 6. A system according to claim 1, characterized in that means are provided for snap-fitting said spacing means into position on said ceiling support members, and in that at least one resilient ratchet-type projection is provided on said spacing means for engagement with the aperture means of said main ceiling support member.
 7. A ceiling support system comprising a plurality of ceiling support members arranged for supporting ceiling panels, spacing means operatively connected to at least two adjacent support members for spacing said at least two adjacent support members a predetermined distance from one another to form a gap therebetween, and supporting guide means for guiding relative movement between the at least two adjacent support members in a horizontal plane, said spacing means including structure constructed of a relatively more fusible material than said support members and said supporting guide means, whereby the fusible structure of the spacing means will melt in the event of a fire permitting the adjacent support members to move in a horizontal plane relatively to one another thereby reducing the risks of buckling and collapse of the ceiling system, wherein at least one of said gaps is located between adjacent ends of adjacent aligned ceiling support members, wherein said spacing means and said supporting guide means include means for permitting relative movement of the aligned ceiling support members in a single axial direction while preventing substantial relative movement in directions other than said axial direction, and wherein said spacing means includes a longitudinal spacing members spanning said gap and a fusible securing member for securing the spacing member to at least one of said ceiling support members, said spacing member operatively engaging both of said adjacent ceiling support members to normally hold said ceiling support members in a fixed position with respect to one another.
 8. A system according to claim 7, characterized in that said spacing member and one of said ceiling support members have registering apertures, and in that said fusible securing members includes a peg-like member inserted through said registering apertures.
 9. A system according to claim 7, characterized in that said spacing member and said ceiling support member have registering apertures, said fusible securing member being bridge shaped for spAnning the respective ceiling support member and including at least one resilient ratchet-type projection engaging in said registering apertures.
 10. A ceiling support system comprising a plurality of ceiling support members arranged for supporting ceiling panels, spacing means operatively connected to at least two adjacent support members for spacing said at least two adjacent support members a predetermined distance from one another to form a gap therebetween, and supporting guide means for guiding relative movement between the at least two adjacent support members in a horizontal plane, said spacing means including structure constructed of a relatively more fusible material than said support members and said supporting guide means, whereby the fusible structure of the spacing means will melt in the event of a fire permitting the adjacent support members to move in a horizontal plane relatively to one another thereby reducing the risks of buckling and collapse of the ceiling system, wherein at least one of said gaps is located between adjacent ends of adjacent aligned ceiling support members, wherein said spacing means and said supporting guide means include means for permitting relative movement of the aligned ceiling support members in a single axial direction while preventing substantial relative movement in directions other than said axial direction, and wherein said adjacent aligned ceiling support members are constructed as channel sections having internal support surfaces within and on each side thereof, said internal support surfaces having recesses thereunder, said supporting means including a sleeve member mounted on the outside of the channel sections and having inwardly projecting bottom lips engaging in said recesses.
 11. A ceiling support system comprising at least one main ceiling support member extending longitudinally along a first axis, two subsidiary ceiling support members arranged at opposite sides of said main member and extending longitudinally along a second axis arranged at an angle with respect to the first axis, and a connecting means operatively connecting said main member to both of said subsidiary members at a position spaced from the ends of the main member, said connecting means including a connecting member having a downwardly open U-shaped configuration straddling the main member such that a connecting leg is disposed on each of two opposite sides of said main member, that portion of the U-shaped connecting member between the connecting legs being fastened to said main member by fastener means engaged in an aperture on said main member, each of said connecting legs being connected to an end of a respective subsidiary member by way of detent means positioned on said subsidiary member and said connecting leg such that the respective ends of the subsidiary members are held in a predetermined distance from vertically extending outer surfaces on said main member, whereby the subsidiary member can move along the second axis said predetermined distance upon disengagement of the connecting means prior to abuttingly engaging said main member.
 12. A system according to claim 11, characterized in that said main member is constructed as a three sided box-shaped channel member with the open side facing downwardly, said channel member including outwardly extending lip portions for slidably supporting bottom end portions of said subsidiary members, and in that said first and second axes are substantially perpendicular to one another and are in a common horizontal plane.
 13. A system according to claim 12, characterized in that said connecting member is constructed of material that is more fusible than the material of the ceiling support members, whereby during a fire the connecting member becomes inoperable and the subsidiary members are permitted to slide freely on the lip portions in the direction of the vertically extending outer surfaces of the main member.
 14. A system according to claim 13, characterized in that said detent means include a cut-out recess portion in the respective subsidiary members and an outer wall portion of the respective connector legs.
 15. A system according to claim 14, characterized in that said fastener means includes a peg-like member having two resilient ratchet type projections for engaging in an aperture at the top of the main member.
 16. A fusible securing device for securing a first ceiling support building member of a three sided rectangular box-shaped configuration with the open side facing downwardly to two further ceiling support building members extending perpendicularly to and at opposite sides of said first member in such a manner as to permit the building members to move with respect to one another upon melting of the fusible device in a fire; said securing device being of a downwardly open U-shaped configuration for straddling said first member with securing legs of said device disposed at each of two opposite sides of said first member, said device further including at least one resilient ratchet-type projection extending downwardly from that portion of the device interconnecting the securing legs for snap-fitting engaging in a corresponding aperture at the top side of the first member, and each of said securing legs having detent parts for engaging with respective detents at the top portions of said further members for holding the further members a predetermined distance from vertically extending outer surfaces at the sides of the first member whereby said device can be inserted from above onto said building members and whereby said further members can move said predetermined distance upon melting of said securing device prior to abutting engagement with said first member.
 17. A securing device according to claim 16, wherein said securing legs each include uprights of hollow section and open at the bottom, and wherein said detent part is an outer wall of said hollow section which is engageable in a detent on the end portion of the respective further member. 